Method for providing at least one work roll for rolling rolling stock

ABSTRACT

The invention relates to a method for providing at least one work roll ( 1, 2 ) for rolling strip-shaped rolling stock ( 3 ), wherein the work roll ( 1, 2 ) is provided to interact with a second roll ( 4, 5 ), particularly with an intermediate or backup roller and be supported by said second roll, wherein the second roll ( 4, 5 ) has a background area ( 6 ) in the axial end regions thereof. In order to improve the quality of a rolled strip, the method according to the invention provides the following steps: a) calculating the roll nip profile resulting between two interacting work rolls ( 1, 2 ), wherein a defined width of the rolling stock ( 3 ) is assumed, which extends at least partially into the region of the background area ( 6 ) of the second roll ( 4, 5 ); b) defining a desired rolling stock contour that is to be created by the rolling process when passing the work rolls ( 1, 2 ); c) calculating a compensation cut for the work roll ( 1, 2 ) by subtracting the defined rolling stock contour according to step b) from the roll nip profile according to step a) and multiplying the calculated difference with a damping factor (K); d) at least partially applying the compensation cut calculated according to step c) to at least one work roll ( 1, 2 ).

The invention concerns a method for preparing at least one work roll for the rolling of preferably strip-shaped rolling stock, wherein the work roll is provided to interact with a second roll, especially an intermediate roll or backup roll, and to be supported by this roll, and wherein the axial end regions of the second roll have a setback.

In particular, when very wide plate is being rolled (e.g., width greater than 3,000 mm), undesired profile shapes sometimes develop in the strip, especially W-shaped profiles and ridge formation near the edges and flatness defects (quarter waves) in the final product.

This can be attributed, among other things, to the fact that during the rolling of wide strips or plates it happens that the outer regions of the rolling stock are located in the area of the setback of the backup rolls or intermediate rolls or, in the case of extended work rolls, actually lie outside the edges of the barrels of the backup rolls or intermediate rolls. The work roll bends back in these regions, and as a result of this, a nonparabolic profile shape can develop in the roll gap, namely, e.g., the aforementioned ridge formation. High rolling forces and work roll bending forces can intensify this effect.

The rolling stock profile is the distribution of the thickness of the rolling stock over its width. Rolling stock profiles that deviates greatly from the parabolic form are generally undesirable, since they can lead to nonflatness in the rolling process or in the downstream processes. In addition, the accuracy to gage of the product can be adversely affected.

The application of roll cuts to work rolls for systematically affecting the roll gap profile is already known. For example, EP 0 294 544 B1 provides that the work roll is provided with a profile that is described by a polynomial. EP 1 307 302 B1 proposes a similar solution, in which a so-called CVC profile is provided. Other similar and different solutions are disclosed in EP 1 703 999 B1, EP 0 937 515 B1, JP 3032412 A, JP 9253726 A, DE 39 19 285 A1, JP 8332509 A, JP 6015322 A, and JP 2179308A. The profiles applied on the work roll are thus parabolic contours or contours described by polynomials. In the latter case, when an axial work roll shifter is present and shifting is used a profile correcting element, the S-shaped contours described by the aforesaid polynomials are applied to the roll (CVC cut).

The application of special contours to reduce edge drop or to reduce ridge formation is also well known. The goal here is to influence the rolling stock profile contour in the immediate edge region in order to compensate effects of work roll flattening in the roll gap or of thermal expansion of the work roll on the roll gap profile.

The prior art cited above does not provide practical advice on how good rolling results can be achieved despite furnishing backup rolls or intermediate rolls with a setback. But this is precisely why the aforementioned problems occur, especially in the case of very wide strips.

Therefore, the objective of the invention is to propose a method for preparing a work roll of the type described at the beginning, with which it is possible, even when there is a corresponding setback of the backup roll or intermediate roll, to achieve optimum rolling, i.e., to roll a strip that is characterized by high quality and the desired shape. Accordingly, undesirable nonparabolic effects of the backup roll or intermediate roll setback on the roll gap profile shape are to be largely compensated. The provision of the work rolls with a special cut (e.g., CVC cut) should not be compromised.

The solution to this problem by the invention is characterized in that the method for preparing at least one work roll for the rolling of preferably strip-shaped rolling stock has the following steps:

(a) computation of the roll gap profile that is formed between two interacting work rolls, where a defined width of the rolling stock is assumed, which extends at least partially into the region of the setback of the second roll;

(b) definition of a desired rolling stock contour that is to be produced by the rolling process during passage through the work rolls;

(c) computation of a compensation cut for the work roll by subtraction of the rolling stock contour defined according to step (b) from the roll gap profile according to step (a) and multiplication of the computed difference by a damping factor;

(d) at least proportional application of the compensation cut computed according to step (c) to at least one work roll.

The compensation cut according to step (c) can be superimposed on another profiling of the work roll. This other profiling of the work roll is preferably a parabolic profiling or an S-shaped profiling (so-called CVC profiling).

The damping factor for the computation according to step (c) is preferably 0.3-0.9 and more preferably 0.4-0.8. A value of 0.6 has been found to be especially effective. The factor is chosen in such a way that for the broad strips or products, ridge-shaped profile forms no longer arise or the ridges are greatly reduced, and for narrower dimensions of the strip, no disturbing effects or only slightly disturbing effects arise.

In accordance with a preferred embodiment, the computation according to step (a) is based on the maximum width provided for the rolling stock that is to be rolled with the work rolls.

The computation according to step (a) is preferably based on a well-defined rolling force and a well-defined work roll bending force. The definition according to step (b) is preferably based on the same parameters as in step (a).

It is advantageous for the profile that is to be defined in accordance with step (b) to be based on a roll gap profile computed offline. In this case, it can be provided that the roll gap profile computed offline is based on an extended backup roll barrel, so that the edges of the rolling stock are not located in the region of the setback of the second rolls.

Accordingly, the proposed method provides a work roll cut to compensate the bending behavior of the work roll in the region of the backup roll setback. A possibly desired special roll cut (e.g., a CVC cut) is superimposed on the compensation cut provided in accordance with the invention.

An essential feature of the proposed cut is that the effect of the setback compensation is almost independent of the axial shift position of the work rolls to each other, so that in the case of shiftability of the work rolls, this effect is effective over the entire shift range.

The compensation cut can be used both on work rolls that can be axially shifted and on work rolls that cannot be shifted.

It can be proportionally applied to only one work roll or to the upper and the lower work roll.

The compensation cut can be combined with any desired roll cut, i.e., it can be superimposed on it. The height of the cut can be varied according to the current work roll diameter. The height can also be adapted to the current backup roll contour or intermediate roll contour (with respect to wear).

The cut can be described, for example, by a sequence of points or by a mathematical function (e.g., by a polynomial function).

The drawings illustrate a specific embodiment of the invention.

FIG. 1 is a schematic drawing of the work rolls and backup rolls of a four-high rolling stand during the rolling of strip-shaped rolling stock, viewed in the direction of rolling.

FIG. 2 shows the variation of the roll gap, i.e., the height of the roll gap over the width less the height in the center, between two work rolls over the width of the rolling stock during the rolling of the rolling stock without the use of the method of the invention.

FIG. 3 shows the variation of the roll gap between two work rolls over the width of the rolling stock as a target contour (ideal profile shape).

FIG. 4 shows the variation of the roll gap between the work rolls over the width of the rolling stock as the difference contour between the target contour according to FIG. 3 and the variation according to FIG. 2.

FIG. 5 shows the variation of a compensation cut for the work rolls over the width of the rolling stock.

FIG. 6 shows the effect of the compensation cut (supplementary cut) over the width of the rolling stock for different axial shift positions on the unloaded roll gap.

FIG. 7 shows the variation of the roll gap between two work rolls over the width of the rolling stock with the use of the compensation cut according to FIG. 5.

FIG. 1 shows two work rolls 1, 2, which are part of a four-high rolling stand (which itself is not shown). The work rolls 1, 2 are supported in a well-known way by backup rolls 4, 5. The rolling stock 3 that is to be rolled, which in the present case is a strip with a width B of 3,100 mm, is located between the work rolls 1, 2.

In their lateral regions, i.e., their axial end regions, the backup rolls 4, 5 have a setback 6, i.e., the profile is set back compared to a pure cylinder. In FIG. 1 this is shown with strong exaggeration.

Accordingly, for the embodiment illustrated here, this has the following consequence: Full support of the work rolls 1, 2 by the backup rolls 4, 5 is provided only in the middle region over a distance of 2,050 mm, since each setback 6 in the two lateral regions extends over a distance of 500 mm. The work rolls, which have a length of 3,450 mm, extend beyond the width B of the rolling stock 3 of 3,100 mm.

The work rolls 1, 2 are acted upon not only by the support forces of the backup rolls 4, 5 but also by work roll bending forces F_(B) and the rolling forces themselves, so that the work rolls experience reverse bending, which is indicated by the arrows 7.

The reverse bending of the work rolls in the area of the setback 6 of the backup rolls thus depends on the rolled width of the rolling stock 3, the rolling force that is applied, and the work roll bending force F_(B) that is set. Therefore, the choice of a frequently rolled large width of the rolling stock and of a mean rolling force that is customary for the last passes of a pass program and a bending force (balancing force) at a low level are advantageous for the cut configuration. In this regard, we can initially proceed from average roll diameters. The roll cambers are chosen in each case in such a way that the computed roll gap profiles fall within the usual range (about 0.000 mm to 0.200 mm).

In a first stop of the work roll configuration or preparation, the roll gap profile to be expected is computed for the rolling stand to be considered under the aforesaid boundary conditions for the maximum width to be rolled. An example of the result of such a computation is shown in FIG. 2. Here we see the shape of the roll gap profile for a rolling stock width of 3,100 mm without compensation of the reverse bending effect. It is clearly seen that the profile takes an undesired course in the lateral region of the strip due to the reverse bending of the work rolls.

After this profile has been determined, an ideal rolling stock contour is defined for the same case. This can be, for example, a roll gap profile computed offline under the assumption of an extended backup roll barrel, so that the edges of the rolling stock are not located in the area of the setback 6 of the backup rolls. This ideal profile shape is shown in FIG. 3 as an example of a target contour, again for a strip with a width of 3,100 mm.

In the next step, the undesired profile component produced by the reverse bending effect is determined by subtracting the target contour (according to FIG. 3) from the roll gap shape without compensation cut (according to FIG. 2). This is illustrated in FIG. 4. Sketched here is thus the difference contour between the target contour and the roll gap shape without compensation, again for a strip with a width of 3,100 mm. The solid curve is the roll gap shape without compensation cut, while the dot-dash curve indicates the target contour. Accordingly, the broken curve represents the difference contour that is needed to compensate the reverse bending effect.

The compensation cut for the work roll is obtained by the difference contour according to FIG. 4, where the difference that is determined is multiplied by a damping factor K of, e.g., 0.7. This factor is chosen in such a way that in the case of broad strips, ridge-shaped profile forms do not arise, while in the case of narrower dimensions of the strip, no disturbing effects or only slightly disturbing effects arise.

The compensation cut for application to both work rolls 1, 2 is shown in FIG. 5. The graph shows the radius deviation (Δr) over the barrel length.

If the compensation cut is to be applied to only one work roll, its height is doubled accordingly.

In the region near the rolling stock towards the edges of the barrel, the contour should run out harmonically, as is indicated in FIG. 5 with reference number 8.

The effect of the supplementary cut on the unloaded roll gap is illustrated in FIG. 6 for different axial shift positions. The solid line indicates the curve that is obtained with work rolls 1, 2 that have not been axially shifted. On the other hand, the broken line shows the curve that is obtained when the upper and lower work rolls are shifted relative to each other by 150 mm. FIG. 6 thus shows the effect on the unloaded roll gap as a function of the axial shift position. It is apparent that even in the case of a relatively large axial shift of the rolls, the desired effect remains largely constant.

Finally, FIG. 7 shows the resultant roll gap shape obtained with the use of the compensation cut. The improvement that is realized in the profile shape is apparent from a comparison of this contour with the original contour without compensation cut according to FIG. 2.

When a six-high rolling stand is used instead of the four-high rolling stand illustrated here, similar results are obtained, but in this case the backup roll is replaced by the intermediate roll.

LIST OF REFERENCE NUMBERS AND LETTERS

-   1 work roll -   2 work roll -   3 rolling stock -   4 second roll (intermediate roll, backup roll) -   5 second roll (intermediate roll, backup roll) -   6 setback -   7 bending direction (reverse bending of work roll) -   8 harmonic runout -   B width of the rolling stock -   K damping factor -   F_(B) work roll bending force 

1-10. (canceled)
 11. A method for preparing at least one work roll for rolling of rolling stock, wherein the work roll is provided to interact with a second roll, and to be supported by the second roll, and wherein axial end regions of the second roll have a setback, wherein the method comprising the steps of: (a) computing a roll gap profile that is formed between two interacting work rolls, where a defined width (B) of the rolling stock is assumed, which extends at least partially into a region of the setback of the second roll; (b) defining a desired rolling stock contour that is to be produced by the rolling process during passage through the work rolls; (c) computing a compensation cut for the work roll by subtracting the rolling stock contour defined according to step (b) from the roll gap profile according to step (a) and multiplying the computed difference by a damping factor (K); and (d) at least proportionally applying compensation cut computed according to step (c) to at least one work roll.
 12. The method in accordance with claim 11, including superimposing the compensation cut according to step (c) on another profiling of the work roll.
 13. The method in accordance with claim 12, wherein the another profiling of the work roll is a parabolic profiling or an S-shaped profiling.
 14. The method in accordance with claim 11, wherein the damping factor (K) for the computation according to step (c) is 0.3-0.9.
 15. The method in accordance with claim 14, wherein the damping factor (K) for the computation according to step (c) is 0.4-0.8.
 16. The method in accordance with claim 11, including basing the computation according to step (a) on the maximum width (B) provided for the rolling stock that is to be rolled with the work rolls.
 17. The method in accordance with claim 11, including basing the computation according to step (a) on a well-defined rolling force.
 18. The method in accordance with claim 11, including basing the computation according to step (a) on a well-defined work roll bending force (F_(B)).
 19. The method in accordance with claim 11, including basing the definition according to step (b) on the same parameters as in step (a).
 20. The method in accordance with claim 11, including basing the definition according to step (b) on a roll gap profile computed offline.
 21. The method in accordance with claim 20, including basing the roll gap profile computed offline on an extended backup roll barrel, so that edges of the rolling stock are not located in the region of the setback of the second rolls. 